The present invention relates to an improved inflatable cuff used for measuring a patient's blood pressure. Blood pressure results from the patient's heart pumping blood through the patient's body. As the heart periodically contracts, blood is forced through the arteries that extend throughout the body. With each contraction of the heart muscle, irregularly shaped pressure pulses propagate through the arteries, causing the arterial walls to flex or oscillate.
Two common methods used to measure a patient's blood pressure are the auscultatory method and the oscillometric method. In the auscultatory method, a cuff having an inflatable bladder associated therewith is secured around the patient's arm and the bladder is inflated. The inflated bladder, secured by the cuff, acts against the patient's arm to completely block the flow of blood through the brachial artery. The pressure in the cuff is then slowly reduced while a stethoscope is used to monitor the distal end of the artery to listen for pulsating sounds, known as Korotkoff sounds, that accompany the re-establishment of blood flow through the artery. The air pressure within the bladder is monitored as the pressure is reduced. The air pressure present in the bladder when Korotkoff sounds first appear is a measure of the systolic pressure, and the pressure in the bladder when the Korotkoff sounds disappear altogether (meaning that unrestricted blood flow has been reestablished) is a measure of the diastolic pressure.
The oscillometric method also employs a pressure cuff, however, rather than listening for the sound of the blood flowing through the artery, the oscillometric method measures blood pressure by measuring the flexing of the arterial wall. When the pressure cuff is inflated around the patient's arm, the flexing of the arteries adjacent the pressure cuff is transmitted to the inflated bladder. The flexing of the arteries causes minute, but detectable, pressure variations or pulses within the bladder which correspond to the flexing of the arteries. These pulses, also known as complexes, are affected by the pressure in the inflatable bladder. When the cuff pressure is approximately equal to the mean arterial pressure (MAP), the peak-to-peak amplitude of the complexes reaches a maximum value. Similarly, the peak-to-peak amplitude of the complexes is at a minimum when the cuff pressure is above the systolic pressure and below the diastolic pressure. Thus, by measuring these complexes at various cuff pressures, the mean arterial pressure and the diastolic and systolic pressures can be approximated.
It should be noted that the methods described above provide a non-invasive method for approximating the actual pressure of the blood flowing through the patient's arteries. The approximations employed in the methods described above are the result of an extensive body of research correlating blood pressure values measured using either the auscultatory or the oscillometric method against actual values obtained using more direct techniques. The majority of this research has been based on blood pressure cuffs having rectangular inflatable bladders. Furthermore, the shape of the bladder has a significant impact on blood pressure readings obtained using either the auscultatory or oscillometric method. Therefore, in order for blood pressure readings taken in the field to conform to the empirical research data, a rectangular inflatable bladder is highly desirable.
A significant number of patients who require regular blood pressure measurements are those suffering from hypertension. Many of these patients also suffer from clinical obesity. Obese patients often have upper arms that are not only large, but also have a characteristic conical shape. This conical shape is also exhibited in some patients having highly developed upper arm musculature.
Common rectangular blood pressure cuffs do not work effectively on patients having upper arms with a pronounced conical shape. When a rectangular cuff is wrapped conformally around the patient's upper arm, the ends of the cuff will overlap in an angular manner to conform to larger diameter of the patient's arm near the shoulder, and the smaller diameter of the arm near the elbow. Inflation of the bladder will cause a twisting movement of the overlapping closure, possibly pinching the patient's skin. If however, the cuff is wrapped as a cylinder conforming to the larger circumference of the patient's arm, a large air gap is formed between the cuff and the smaller circumference of the patient's upper arm at the opposite end. When the bladder is filled with air, a much larger volume of air is required to fill the lower portion of the bladder than is necessary to fill the upper portion. This too can lead to patient discomfort and, more importantly, inaccurate blood pressure readings. A further disadvantage to wrapping the blood pressure cuff in this manner is that the cuff tends to slide down the patient's arm due to the minimal surface area of skin contacting the cuff.
To resolve this problem, conical blood pressure cuffs have been developed. Existing conical cuffs include a separate bladder element which is inserted into a pocket located within the cuff. Both rectangular and conical bladder elements have been employed. However, conical bladders do not conform to the immense body of research that has been conducted based on rectangular bladder elements. Furthermore, the final dimensions of the bladder are defined by the size of the cuff pocket which constrains the bladder when the bladder is inserted and inflated therein. For conical cuffs with separate bladder elements, even rectangular bladder elements, the pocket tends to distort the natural inflated shape of the bladder, resulting in a deformed bladder shape that does not conform with the dimensional test data for rectangular bladders. What is more, the two component design is cumbersome to use and can lead to inaccurate readings.
Therefore, a need exists for a fully integrated conical blood pressure cuff wherein the inflatable bladder is formed directly with the cuff. Furthermore, in order for the readings obtained by such an integrated conical blood pressure cuff to conform to the large body of research data regarding blood pressure measurement, it is desirable that the integrated bladder have and retain a rectangular shape, even when conformally applied to a patient's conically shaped upper arm and inflated therearound.